You may be imagining that it will be complete OS/systems written in non-C language from scratch, but it doesn't have to happen that way.
With languages with no GC or optional GC, calling back and forth between the new language and C is easy and direct, and so writing only new (or maybe historically problematic) pieces of a system in the new language becomes feasible.
With languages with no GC or optional GC, calling back and forth between the new language and C is easy and direct, and so writing only new (or maybe historically problematic) pieces of a system in the new language becomes feasible.